An image sensor is a device for converting an optical image to an electric signal. Image sensors may be categorized into a complementary metal-oxide-silicon (CMOS) image sensor and a charge coupled device (CCD) image sensor.
The CCD image sensor is considered superior to the CMOS image sensor in characteristics of photosensitivity and noise but has difficulty in achieving highly integrated density and reducing its high power consumption. On the contrary, the CMOS image sensor has simpler processes than those of the CCD image sensor and may be more suitable for achieving highly integrated density and reducing its power consumption.
As semiconductor device fabricating technology has become more highly developed, efforts are actively made to research and develop the CMOS image sensor due to improved fabricating technology and characteristics of CMOS image sensors.
A pixel of a CMOS image sensor may include a plurality of photodiodes for receiving light and CMOS devices for controlling the received light. Electron-hole pairs may be generated in the photodiodes according to wavelength and intensity of red, green and blue rays incident via a color filter. As an output signal varies according to a quantity of the generated electrons, an image can be sensed.
An image sensor such as a CMOS image sensor may include a pixel area for accommodating a photocharge converting unit such as a photodiode and a peripheral circuit area for detecting signals output from the pixel area. In particular, the peripheral circuit area may be provided to surround the pixel area.
As illustrated in example FIG. 1, a device provided with the above-configured CMOS image sensor may use a metal such as tungsten (W) and the like as dark shield layer 4 for cutoff and anti-reflection of light in a visible ray area. Dark shield layer 4 formed of a thin layer of tungsten may be advantageous in blocking the light transmittance effectively. If so, however, interactive capacitance may increase between upper metal line 2 and dark shield layer 4.
A process for forming dark shield layer 4 may be difficult in performing alignment for defining the dark shield layer. Moreover, upper metal line 2 and dark shield layer 4 may be formed spatially too close to each other, whereby parasitic capacitance increases.